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Hog Fuel (Wood Waste) Boiler Feed Metering Bins

Hog Fuel (Wood Waste) Boiler Feed Metering Bin

 

This case study highlights the retrofit of four live bottom metering bins that were suffering from chronic plugging at a pulp mill in Port Angeles, Washington State. Kamengo replaced the four metering bins with new bins, Kamengo Feeders, chute and expansion joint. Prior to the retrofit, the plant was experiencing lost steam production and swings in the header pressure, which made it particularly problematic to keep emissions within the plant’s permit. Post retrofit, the plant is producing more steam, and the boiler is able to meet the changing steam demands from the paper plant while maintaining an even header pressure. The retrofit was completed in 2015.

The Challenge

Prior to the retrofit, the pulp mill had four live bottom metering bins, each discharging into one of four spouts into the boiler.

 

Each metering bin consisted of two augers below a negative taper storage bin. Although the boiler was only two years old, the mill was keen to improve the reliability fuel feed into the boiler. The screw feeders had a propensity to compact material at the front of the bin walls as well as rat hole in the storage bin. The mill tried a number of solutions, including installing UHMW along the front of the bin walls. Nothing worked.

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Why the Conventional Screw Feeders Were Suffering from Chronic Plugging and Inconsistent Discharge

The screw augers were suffering from chronic plugging for two reasons:

 

First, the screw augers have a tendency to compact material against the front of the bin wall. Wood waste that is being carried or sheared from the storage bin, through friction or interlocking, carries fuel above it. And this fuel travelling above the screw feeder outlet is compacted against the bin wall. The problem is that wood waste gains significant strength when it is compacted. Once the fuel above the outlet gains sufficient strength it will bridge over the outlet resulting in inconsistent discharge and plugging.

 

Second, the screw augers withdraw material primarily from the rear of the bin. This limited withdrawal of material has several consequences. First, it means that gravity is acting on a smaller area than the total footprint of the screw auger, leaving a stagnant pocket of material at the front of the bin. This tagnant material is allowed to compress and compact over time under its own weight. The more wood waste compacts, the stronger it gets. Eventually the material will be strong enough to form a stable bridge. Second, the uneven withdrawal of fuel by the screw auger promotes a funnel flow discharge pattern, which promotes rat-holing, which will lead to plugging through the center of the bin.

Kamengo’s Solution

In contrast to the screw feeders, the Kamengo Feeder withdraws material evenly from its full opening, while avoiding the compaction that promotes material bridging. Because the Feeder withdraws material evenly from its entire opening, all of the material above the feeder is in motion during discharge, resulting in a mass flow, or first-in, first-out discharge. Handling a low bulk density, easily compactible bulk solid like wood waste in mass flow is important to ensuring a reliable system.

Finally, the Kamengo Feeder delivers a very steady, predicable discharge of fuel into the boiler. This is necessary for maintaining a predictable pyrolytic reaction in the boiler. The steady discharge of fuel from the Kamengo Feeders improved boiler efficiency and resulted in higher steam-output with lower emissions.

 

To minimize disruption to structural steel and the existing slide gates between the distribution chain conveyor and the metering bins, Kamengo kept the upper half of the existing metering bins and replaced everything to the boiler distributor. For each metering, Kamengo supplied a new lower half storage bin, Kamengo Feeder, collection screw conveyor, screw conveyor discharge chute and expansion joint.

 

The screw conveyor is required because the Kamengo Feeder discharges material across its full length. There is no head of material above the screw auger – in fact the screw trough is never more than 1/3 full and only requires a 5HP drive. As such the screw is only acting as a conveyor and not as a feeder.  Although the screw conveyor introduces an additional mechanical item, its inclusion permits a layout that maximizes storage at the boiler.

Learn More

To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please download our white paper entitled: The Design of Reliable Storage Bins and Feeders for the Biomass Industry. 

Hog Fuel (Wood Waste) Boiler Feed Metering Bins

Hog Fuel (Wood Waste) Boiler Feed Metering Bins 

This case study highlights the retrofit of eight small screw feeders experiencing chronic plugging at a mill in Quesnel, BC. The screw feeders where replaced by four surge bins and feeders. Each Kamengo Feeder feeds a split chute, which in-turn directs the hog fuel into two boiler spouts. Prior to the retrofit, the plant was experiencing lost steam production and swings in the header pressure. Post retrofit, the plant is producing more steam, and the boiler is able to meet the changing steam demands from the paper plant while maintaining an even header pressure. The retrofit was completed in 2015.

The Challenge

Prior to the retrofit, the pulp mill had eight small screw feeders that were experience chronic plugging. Each screw feeder consisted of a single auger with a very small and narrow storage bin above it. Although the mill limited the head of material above the screw augers, the metering bins were very unreliable.

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Why the Conventional Screw Feeders Were Suffering from Chronic Plugging and Inconsistent Discharge

The screw augers were suffering from chronic plugging for two reasons:

 

First, the screw augers have a tendency to compact material against the front of the bin wall. Wood waste that is being carried or sheared from the storage bin, through friction or interlocking, carries fuel above it. And this fuel travelling above the screw feeder outlet is compacted against the bin wall. The problem is that wood waste gains significant strength when it is compacted. Once the fuel above the outlet gains sufficient strength it will bridge over the outlet resulting in inconsistent discharge and plugging.

 

Second, the screw augers withdraw material primarily from the rear of the bin. This limited withdrawal of material has several consequences. First, it means that gravity is acting on a smaller area than the total footprint of the screw auger, leaving a stagnant pocket of material at the front of the bin. This tagnant material is allowed to compress and compact over time under its own weight. The more wood waste compacts, the stronger it gets. Eventually the material will be strong enough to form a stable bridge. Second, the uneven withdrawal of fuel by the screw auger promotes a funnel flow discharge pattern, which promotes rat-holing, which will lead to plugging through the center of the bin.

Kamengo’s Solution

In contrast to the screw feeders, the Kamengo Feeder withdraws material evenly from its full opening, while avoiding the compaction that promotes material bridging. Because the Feeder withdraws material evenly from its entire opening, all of the material above the feeder is in motion during discharge, resulting in a mass flow, or first-in, first-out discharge. Handling a low bulk density, easily compactible bulk solid like wood waste in mass flow is important to ensuring a reliable system.

 

Finally, the Kamengo Feeder delivers a very steady, predicable discharge of fuel into the boiler. This is necessary for maintaining a predictable pyrolytic reaction in the boiler. The steady discharge of fuel from the Kamengo Feeders improved boiler efficiency and resulted in higher steam-output with lower emissions.

Learn More

To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please download our white paper entitled: The Design of Reliable Storage Bins and Feeders for the Biomass Industry. 

Hog Fuel (Wood Waste) Boiler Feed Metering Bins

Hog Fuel (Wood Waste) Boiler Feed Metering Bins  

 

This case study is an example of a retrofit of wood waste or hog fuel metering bins that are metering fuel into a power boiler. The retrofit was completed in 2015.

The Challenge

Prior to the retrofit, the pulp mill had a single live bottom bin discharging into five inlets. The bin suffered from chronic plugging causing the mill to either burn gas at a high expense or live with a lower steam output and lower pulp production. To minimize plugging issues, the mill was forced to run the live bottom bin with a very low head of fuel.

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Why the Existing Conventional Screw-Type Feed Bins Were Suffering from Chronic Plugging and Inconsistent Discharge

The live bottom bin suffered from many of the challenges typical of conventional feeders. First, the screw augers have a propensity to compact material against the front of the bin wall. As wood fuel is sheared from the storage bin, due to interlocking and friction, the fuel being carried out carries fuel above it. And this fuel travelling above the outlet is compacted against the bin wall. The problem is that wood waste gains significant strength when it is compacted. Once the fuel above the outlet gains sufficient strength it will bridge over the outlet resulting in inconsistent discharge and plugging. Second, the screw augers withdraw material from the back of its opening, leaving a stagnant pocket of material at the front. This limited withdrawal of material has several consequences. First, it means that not only is gravity acting on a smaller area, but it also means that the stagnant material is allowed to compress and compact over time under its own weight. The more wood waste compacts, the stronger it gets. Eventually the material will be strong enough to form a stable bridge. Second, uneven withdrawal promotes a funnel flow discharge pattern, which promotes rat-holing.

Kamengo’s Solution

In contrast to the live bottom bin, the Kamengo Feeder withdraws material evenly from its full opening. Further, the opening of a Kamengo Feeder can be made as wide as needed and as long as desired. For this retrofit, Kamengo replaced the live bottom bin with five individual metering bins, each with its own Kamengo Feeder. Because the Kamengo Feeder withdraws material evenly from its entire opening, all of the material above the feeder is in motion during discharge, resulting in a mass flow, or first-in, first-out discharge. Handling a low bulk density, easily compactible bulk solid like wood waste in mass flow is important to ensuring a reliable system.

 

Finally, the Kamengo Feeder delivers a very steady, predicable discharge of fuel into the boiler. This is necessary for maintaining a predictable pyrolytic reaction in the boiler. The steady discharge of fuel from the Kamengo Feeders improved boiler efficiency and resulted in higher steam-output with lower emissions.

Learn More

To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please download our white paper entitled: The Design of Reliable Storage Bins and Feeders for the Biomass Industry. 

Hog Fuel (Wood Waste) Tall Day Bin Retrofit

Hog Fuel (Wood Waste) Tall Day Bin Retrofit

 

This case study is an example of a retrofit of a 37-foot tall, 6,000 cu-ft silo used to store and feed hog fuel (wood waste) into a power boiler. The hog fuel at the mill is particularly challenging because it contains hickory bark and can be very stringy.

When Kamengo first met the mill, the plant engineers were exploring options to replace the entire hog fuel feeding system. However, upon learning of a retrofit to a similar size tall bin that Kamengo had completed for a pulp mill in Washington State, USA, the mill found that it could solve its feed issues by retrofitting its existing bin

 

Kamengo replaced the lower half of the bin with a rectangular plane-flow mass flow hopper and Kamengo Feeder. The Kamengo Feeder is ahead of a live bottom bin with screw feeders feeding biomass fuel into the boiler. Since the screw feeders cannot maintain a significant head of material above them, the Kamengo Feeder is used to reliably meter just enough material that the screw feeders can handle to ensure good, steady material discharge into the boiler.

 

This retrofit was completed in 2004.

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Why the Existing Storage and Feed System is Suffering from Chronic Bridging and Inconsistent Discharge

Prior to the retrofit, the storage silo converged with a 60-deg cone down to a vibrating hat. The mill could not put more than 6-feet of material in the storage bin before it would plug. This was problematic, because this storage silo was providing critical storage between the hog fuel pile and the power boiler’s metering bins.

The existing silo was suffering from chronic plugging for three reasons:

  1. Poor bin geometry. The sloping walls and discharge opening of the cone were insufficient to produce a reliable mass flow or first-in, first-out discharge pattern. First, the sloping walls were too shallow. As a result, material could not slide along the hopper walls, but would instead try to slip within itself in a funnel flow, or first-in, last-out discharge pattern. Second, the discharge opening was too small. The smaller the opening, the less strength a material requires to form a stable arch over the bin outlet that gravity cannot reliably break.
  2. The vibrating feeder withdrew material unevenly from the storage bin – pulling material primarily from around the silo walls, leaving behind a relative stagnant core of fuel. This selective withdrawal of material, in addition to the shallow sloping walls, induced a funnel flow, or first-in, last-out discharge pattern in the bin. In principle, there is nothing wrong with funnel flow as long as the effective opening of the bin exceeds the bulk solid’s piping dimension (or distance over which the bulk solid can form a stable rat-hole). Unfortunately, the piping dimension for wood waste is quite large – in fact, it is larger than the silo diameter. To handle hog fuel (wood waste) reliably without hang-ups, it must be discharged in a mass flow, or a first-in, first-out discharge pattern – where all the material in the storage bin descends as a single body and where all the material in the storage bin is in motion. To do achieve a mass flow discharge pattern, the Feeder must withdraw material evenly from the storage bin’s full discharge outlet.

Kamengo’s Solution

The solution to fixing the silo had two parts:

 

The first half of the solution is to modify the bin geometry of the silo such that it will promote a first-in, first-out discharge pattern. In this case, Kamengo cut off the bottom portion of the silo, including the cone and replaced it with a plane flow, mass flow hopper and Kamengo Feeder. A plane flow hopper is the most conservative hopper shape.

 

The new hopper converged to wide and long 6-foot wide by 18-foot long discharge opening. This wide and long opening is required to ensure gravity will always be sufficient to break the strength of the arch that hog fuel would create above the Feeder. In summary, by replacing the cone with the new plane flow hopper, Kamengo fixed the geometry of the silo such that if the Feeder were removed, the silo would self-empty with only the aid of gravity. The minimum geometry required for gravity discharge, including minimum slope angle of the plane flow hopper and minimum discharge opening were all selected based on the flow properties of hog fuel.

 

The second half of the solution was to pair the plane flow hopper with a fully-effective Feeder – in this case a Kamengo Feeder. A fully-effective feeder is one that withdraws material evenly from its entire opening, which by definition is necessary to actually achieve a mass flow discharge pattern in the hopper. By definition, to achieve mass flow, the bulk solid must descend the storage bin as a single body with all the stored material in motion, and the only way to achieve this is for the feeder to withdraw material evenly from its entire opening. If the Feeder withdraws material selectively from the bin discharge outlet, sections of material in the bin will be stagnant and funnel flow will ensue.

 

Again, discharging in mass flow is often necessary when handling a difficult flowing bulk solid. What makes the Kamengo Feeder unique is that it can be made as wide as needed and as long as desired. This feature is particularly valuable given that the chosen minimum discharge opening of the silo is 6-foot by 18-foot. To achieve mass flow, the Feeder inlet must match this outlet. This is very difficult to do with conventional technologies, but very easy to achieve with a Kamengo Feeder.

Learn More

To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please download our white paper entitled: The Design of Reliable Storage Bins and Feeders for the Biomass Industry. 

Hog Fuel (Wood Waste) Boiler Feed Metering Bins

Hog Fuel (Wood Waste) Boiler Feed Metering Bins

This case study is an example of a retrofit of wood waste or hog fuel metering bins that are metering fuel into two power boilers. The retrofit was completed in 1994.

 

In 2021, Kamengo replaced its previously supplied metering bins with new wider and longer Feeders capable of handling more difficult flowing fuels including roadside slash and long stranded cedar.

Existing System Prior to the Retrofit

Prior to the retrofit, the pulp mill had twelve star feeders, each feeding a separate spout into one of two boilers. In 1993, the pulp mill retrofitted one star feeder with a small Kamengo Feeder. While the star feeders continued to struggle, the Kamengo Feeder proved that it could deliver consistent discharge without hang-ups. In 1994, the pulp mill retrofitted the remaining eleven metering bins with new Kamengo Feeders, hoppers and chutes.

 

By 2021, the originally supplied Kamengo equipment reached its end-of-life. However, instead of replacing the Feeders as they were, Kamengo opted to replace the metering bins to include larger, wider Feeders. These new Feeders are capable of handling much worse fuels including roadside slash and long, stringy cedar.

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Why the Existing System Suffered From Chronic Plugging

Prior to the retrofit, the pulp mill struggled with the star feeders. They suffered from chronic plugging which impacted both emissions and steam-output. Star feeders suffer from two problems. The first problem, is that like most rotary feeders, they withdraw material from a relatively small footprint. Remember, gravity is acting on the area in which material is discharging. When the area through which material is flowing is small, the opening may not be sufficient for gravity to break the strength of the material and keep it flowing. The second problem is that star feeders have a propensity to withdraw material from the back of its opening, leaving a stagnant pocket of material at the front. This limited withdrawal of material means that not only is gravity acting on a smaller area, but it also means that the stagnant material is allowed to compress and compact over time under its own weight. The more wood waste compacts, the stronger it gets. Eventually the material will be strong enough to form a stable bridge.

Kamengo’s Solution

In contrast to the star feeders, the Kamengo Feeder withdraws material evenly from its full opening. Further, the opening of a Kamengo Feeder can be made as wide as needed and as long as desired. For this retrofit, Kamengo is using Feeders with a 3-foot by 7-foot opening, which is several times the footprint of the star feeder. And because the Feeder withdraws material evenly from its entire opening, all of the material above the feeder is in motion during discharge, resulting in a mass flow, or first-in, first-out discharge. Handling a low bulk density, easily compactible bulk solid like wood waste in mass flow is important to ensuring a reliable system.

 

Finally, the Kamengo Feeder delivers a very steady, predicable discharge of fuel into the boiler. This is necessary for maintaining a predictable pyrolytic reaction in the boiler. The steady discharge of fuel from the Kamengo Feeders improved boiler efficiency and resulted in higher steam-output with lower emissions.

Learn More

To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please download our white paper entitled: The Design of Reliable Storage Bins and Feeders for the Biomass Industry. 

Retrofit of Wood Chip Chute Suffering From Chronic Plugging

Retrofit of Wood Chip Chute Suffering From Chronic Plugging  

 

This is an example of when a chute becomes a hopper, and when a conveyor becomes a feeder and plugging ensues.

Why the Chute is Suffering from Chronic Plugging and Bridging

In contrast to a bin or hopper, a chute is where material is continuously flowing and there is no head of material at the outlet. When a chute is flooded such that a head of material builds at the outlet, the chute becomes a hopper and the conveyor on which it discharges onto becomes a feeder. This is problematic because suddenly the chute is subject to minimum geometry constraints needed to avoid bridging and the conveyor needs assume the job of shearing material from the chute.

 

This is an example where the chute is receiving a flood of material from processes upstream causing a head of material to build in the chute. And because the geometry of the chute is insufficient to act as a hopper, the chute is subject to chronic plugging and is a major headache for the plant.

 

In summary, because it is carrying a head of material, the chute is not actually a chute, but a hopper and as such, its geometry, including outlet and sloping walls must be sufficiently large and steep to ensure reliable gravity discharge. However, with its four sloping walls and small discharge opening, the chute’s (turned hopper’s) geometry is insufficient, and hence it is subject to chronic plugging.

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Kamengo’s Solution

The easy solutions to fixing these chutes turned hoppers is to either decrease the discharge of material upstream or increase the speed of the conveyor to ensure no head of material builds up in the chute. If the easy solutions are not viable, as in the case of this case study, the plant needs to install a hopper and feeder designed to handle the bulk solid as an intermediary between the chutes and the conveyor.

 

Choosing a suitable storage and feed system has two components. The first is to choose a bin shape with a wide and long opening, where if the feeder were removed, the hopper would self-empty with only the aid of gravity. Kamengo typically suggests a plane flow hopper (which is a bin shape where the hopper walls only converge in one plane at a time). The plane flow hopper is the most conservative hopper shape.

 

The second half of the solution is to pair the plane flow hopper with a fully effective feeder – that is a feeder that withdraws material evenly from its entire opening – which is necessary for reliable discharge when metering a difficult flowing material from a small hopper. The Kamengo Feeder is a very good choice because not only is it a fully effective feeder, but it can also be made as wide as needed and as long as desired, which opens the range of solutions to fixing a problem storage and feeder system.

Learn More

To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please visit KamengoU.

Limestone Surge Bin Retrofit

Limestone Surge Bin Retrofit 

This is an example of a limestone bin that is suffering from chronic bridging. It is a good example of an instance where the behavior of the Feeder is inducing rat-holing and bridging despite the fact that the bin is constructed with correct geometry.

The Existing Storage and Feed Arrangement and Why it is Suffering from Chronic Plugging and Inconsistent Discharge

The existing bin consists of several stacked chisel hoppers, and is discharged using a slide gate that opens from the middle outwards. To control the discharge onto the conveyor below, the slide gate opening is incrementally adjusted. Unfortunately, the system suffers from chronic rat-holing and bridging.

 

In summary, the bin is suffering from chronic plugging because when the slide gate is only partially open it induces a funnel flow discharge pattern despite the fact that the geometry of the storage bin is correct, where if the slide gate were removed, the bin would self-empty in a mass flow or first-in, first-out discharge pattern. Funnel flow (which is a first-in, last-out discharge pattern) can be made to work with a large discharge outlet. However, when the discharge outlet is small, gravity is insufficient to overcome the strength of the bulk solid at the discharge outlet, and hence chronic bridging and rat-holing is expected.

 

As noted, the storage bin is designed to discharge in a mass flow, or first-in, first-out discharge pattern. The definition of mass flow is that during discharge, the entire mass of stored material comes down as a single body (single mass). To achieve this, material must discharge evenly from the entire discharge outlet of the storage bin. The tell-tale sign that you have mass flow is that material is sliding down the bin walls. In contrast, with funnel flow, material is stagnant along the hopper walls. When the slide gate is only partially open, then material is not permitted to withdraw evenly from the entire discharge outlet of the storage bin because the slide gate has limited the “live” opening. The result is stagnant material along the bin walls and a funnel flow discharge pattern.

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Kamengo’s Solution

The solution to fixing this problem bin is simple. Given that the bin geometry is correct, such that if the Feeder were removed, the entire bin would self-empty with gravity in a mass flow or first-in, first-out discharge pattern, only the behavior of the Feeder needs to be fixed. In this case, the feeder must be fully effective, which means that it must withdraw material evenly from its entire opening. The attached solution pairs the bin with a Kamengo Feeder. The reason for doing so is that the Kamengo Feeder withdraws material evenly from its entire opening, which by definition is necessary to actually achieve a mass flow discharge pattern in the bin.

Learn More

To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please visit KamengoU.

Hog Fuel (Wood Waste) Tall Day Bin

Hog Fuel (Wood Waste) Tall Day Bin

This is an example of a storage bin designed specifically to handle difficult flowing biomass, including stringy woody biomass.

Why Conventional Live Bottom Bins Suffer from Chronic Plugging and Inconsistent Discharge

Standard storage bins used to handle biomass are typically negative taper, and use a live bottom reclaim system such as augers or a stoker.

In summary, live bottom negative taper bins struggle handling biomass because: 1) they allow the stored biomass to compact on itself and place a heavy load on the reclaim system, 2) promote material compaction by driving material against the bin front wall, and 3) withdraw material in a funnel flow discharge pattern, which induces rat-holing.

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Kamengo’s Solution

The solution to a reliable biomass storage bin starts with good bin design and moving away from the negative taper bin to a positive taper bin where the majority of the load in the bin is carried by the bin walls, and where the biomass will accelerate from the storage bin during discharge. However, for reliable discharge, the geometry of the positive taper storage bin must be correct. The most conservative bin shape for handling biomass is a plane flow hopper shape with a wide and long discharge opening. A plane flow hopper only converges in one plane at a time, and is vertical in the opposite plane. The plane flow hopper is the most conservative hopper shape. The purpose of using a conservative bin shape with a long and wide discharge outlet is to employ a geometry where if the Feeder were removed, the entire bin would self-empty with gravity in a mass flow or first-in, first-out discharge pattern.

 

The second half of the solution is to pair the plane flow hopper with a fully-effective feeder – that is a feeder that withdraws material evenly from its entire infeed opening. By definition, to achieve mass flow, where the stored material comes down as a single body, the feeder must withdraw material evenly from its entire opening. If the Feeder withdraws material selectively from the bin discharge outlet, sections of material in the bin will be stagnant and funnel flow will ensue.

 

A great example of a fully-effective feeder is the Kamengo Feeder. In addition to being fully-effective, the Feeder offers consistent metering, and can be made as wide as needed and as long as wanted. As a result, the Kamengo Feeder offers valuable advantages when designing for a difficult flowing fibrous material.

Learn More

To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please download our white paper entitled: The Design of Reliable Storage Bins and Feeders for the Biomass Industry. 

Hot Lime Silo Retrofit

Hot Lime Silo Retrofit

This is an example of a hot lime silo that is suffering from chronic bridging. It is a good example of poor bin geometry combined with uneven discharge that is resulting in chronic bridging.

Why the Existing Storage and Feed Arrangement is Suffering from Chronic Plugging and Inconsistent Discharge

The existing bin consists of a 25-foot diameter silo and 55-deg cone that converges to a 2-foot diameter opening that is fitted with a basket gate.

 

In summary, the silo is suffering from chronic plugging because the shallow cone and the behavior of the basket gate are inducing a funnel flow discharge pattern. Funnel flow (which is a first-in, last-out discharge pattern) can be made to work with a large discharge outlet. However, when the discharge outlet is small, gravity is insufficient to overcome the strength of the bulk solid at the discharge outlet, and hence chronic bridging and rat-holing is expected.

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Kamengo’s Solution

The solution to fixing this problem storage and feed system has two parts. The first half of the solution is to replace the bottom half of the cone with a mass flow chisel hopper with a wide and long opening. The result is an expanded flow bin, with the lower half of the storage silo emptying in mass flow and upper portion emptying in funnel flow. As long as the funnel flow portion is emptied completely on a regular basis the storage bin geometry will be reliable.

 

Mass flow is a first-in, first-out discharge pattern. The definition of mass flow is that during discharge, the entire mass of stored material comes down as a single body (single mass). The tell-tale sign that you have mass flow is that material is sliding down the bin walls. To achieve this, material must discharge evenly from the entire discharge outlet of the storage bin. This requirement leads to the second half of the solution.

 

The second half of the solution is to pair the plane flow chisel hopper with a fully-effective feeder – that is a feeder that withdraws material evenly from its entire infeed opening. Again, by definition, to achieve mass flow, where the stored material comes down as a single body, the feeder must withdraw material evenly from its entire opening. If the Feeder withdraws material selectively from the bin discharge outlet, sections of material in the bin will be stagnant and funnel flow will ensue.

 

A great example of a fully-effective feeder is the Kamengo Feeder. In addition to being fully-effective, the Feeder offers consistent metering, and can be made as wide as needed and as long as wanted. As a result, the Kamengo Feeder offers valuable advantages when designing for a difficult flowing material.

Learn More

To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please visit KamengoU.

Lime Silo Retrofit

Lime Silo Retrofit

This is an example of a solution to fix a lime bin that is suffering from chronic bridging.

Why the Existing Silo is Suffering From Chronic Plugging and Inconsistent Discharge

The existing bin is a silo with a steep cone that converges to a vibratory feeder. The vibratory feeder employs a shallow cone and a small outlet.

 

In summary, the silo is suffering from chronic plugging because the shallow cone of the vibratory feeder is inducing a funnel flow discharge pattern, while constricting the material discharge to too small an opening. Funnel flow (which is a first-in, last-out discharge pattern) can be made to work with a large discharge outlet. However, when the discharge outlet is small, gravity is insufficient to overcome the strength of the bulk solid at the discharge outlet, and hence chronic bridging and rat-holing is expected.

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Kamengo’s Solution

The solution to fixing this problem bin has two parts. The first half of the solution is to rip out the funnel flow cones, and replace them with a steeper mass flow cone and mass flow chisel hopper. Doing so fixes the geometry of the silo such that if the Feeder were removed, the entire bin would self-empty with gravity in a mass flow or first-in, first-out discharge pattern. The second half of the solution is to pair the new cone and hopper with a Kamengo Feeder. The reason for doing so is that the Kamengo Feeder withdraws material evenly from its entire opening, which by definition is necessary to actually achieve a mass flow discharge pattern in the silo. If the Feeder instead withdrew material unevenly, a funnel flow discharge pattern would ensue (regardless of the bin geometry), and rat-holing would occur.

Learn More

To learn more about the physics of storage bin and feeder design as well as the root causes of bin plugging, please visit KamengoU.